The CNC spindle I ordered off AliExpress arrived. It is a little heavier and more industrial than I imagined. As seems to be my modus operandi, I did not really know what I had ordered until it arrived.
- A big motor/ spindle. Turns out it’s a 3-phase induction motor. I’d read somewhere that motors could run off AC (and that the ones in washing machines do) but I think my school electronics ended at DC motors. Having a 4HP 3-phase motor sitting in front of me bamboozled (and scared ) me. There are no instructions.
- A chunky aluminium holder for the spindle (more weight).
- A Variable Frequency Driver (VFD): A Huanyang Inverter which I think is the most common one for CNC spindles. It does have an instruction manual, titled “the use of manual”.
- No wire to go between the motor and the VFD, just a weird 4-pin plug that connects into the top of the spindle (and delivers the our frequency-modulated 3-phase power to it).
- A dozen collets for holding bits in motor (that’s okay) and the holding nut, which looked like it was damaged – see below.
- A submersible water pump for a garden goldfish pond – for cooling the spindle.
Where to start?
“What are AC motors (vs DC)”, “What 3-phase power is (vs regular two-phase)” and “What’s a VFD” all seem like a good start.
What I learnt about induction motors, three-phase power and what the VFD does.
I am none the wiser why you’d use an induction motor over a DC one (or vice-versa).
If you google it, you get a lot of unsatisfactory answers championing both causes. I am not sure people who know the answer to that question post on websites where these things are debated. Tesla use induction motors in their cars (from a DC battery), Toyota Priuses use brushless DC motors.
This article from the Telsa blog is probably as good a comparison as a layman like me is going to get. As the article notes, Nikola Tesla did invent the three-phase induction motor so perhaps Telsa Motors potentially could have a little of a bias? Anyway, despite this, the article concludes ‘either – or’ for AC vs DC.
My limited knowledge of induction motors can be summarised thus:
- They don’t have permanent magnet or brushes. The rotation is generated by induction. Regular DC motors have brushes and magnets. Brushless DC motors, just magnets.
- They are super-common (bathroom fans, washing machines, dryers etc). Which makes sense, 45% of worldwide electric power is used by motors, and most (pretty much all) electric power is delivered as AC. Indeed, the aforementioned article from Tesla says:
The fact that induction motors are directly compatible with conventional utility power is the main reason for their success
- They can run on single phase (i.e. most on the ones in a home) or three phase (or whatever phase) – depending on what they are designed for
- They rotate at a speed proportional to the incoming alternating current frequency. So many induction motors in use do one speed, and one speed only….until you stick in a VFD…
Variable Frequency Drives (VFD)…
- Produce alternating current at varying frequencies (three-phase here) so the rotation speed of an induction motor can be changed and controlled.
- Some/most(?) VFDs (the one I have bought anyway) convert the incoming (single frequency) AC to DC with a rectifier, and then (using magic) produce the (three phase in this case) AC from this DC – perhaps with an inverter? Which means your single phase input AC comes out as three phase power from (my) VFD. Woohoo!!!! I think my VFD does take three phase power input too if I had it…
- Utility power, in most places around the world, is three-phase. There are exceptions, for instance, a few US states do single phase. I read Russia went with DC power for a bit – its AC 220V 50Hz now. Wrong (though maybe not incorrect) call USSR: sitting there watching Betamax on your DC power.
- Why three-phase power for main utility power transmission? From what I understand, it carries more power in fewer wires with lower losses. Which is why you’d want it powering your industrial induction motors too.
- Why two-phase power for mains around the house? Two wires are simpler and cheaper.
Wiring my Spindle (for Power)
Did any of the above help with my wiring my spindle? Not really.
I decided to email the guy, Evon from China who sold it to me. He emailed a day or so later with a video and pin diagram for the connector plug. Evon’s video and plug diagram below:
I am not going to post photos of my connections:
- I don’t what anyone copying me and either smoking the spindle or their heart/house/family.
- The DIY/ unconfirmed expert electrics fraternity on the net are not very friendly:
I can say I have three main wires going in (2-phase wires and earth) and three (three-phase and earth) coming out to the motor. I added an earth to the motor because it seemed like a grown-up thing to do and the control software I am going to uses an earth to probe for the CNC tool bit zero position (the actual reason).
The ‘Damaged’ holding nut
I mentioned before that I wondered if my holding nut was damaged.
Evon from China, said the nicks out of the spindle collet holding nut balance the spindle. I would love to see how that is done. I am going to accept that as an answer from Evon.
I did wonder if on my next trip to China I could just rock up at the factory – surprise Evon – maybe have a meat tea with him?
The fish tank pump
I have this sitting in a sealed tub of coolant (water + car radiator coolant additive). This is circulated through the spindle.